Manufacturing method, control device, and manufacturing apparatus of optical fiber

ABSTRACT

A manufacturing method of an optical fiber includes drawing an optical fiber preform and forming a bare optical fiber, coating an outer circumference of the bare optical fiber with a coating layer including a resin, and holding the bare optical fiber using one or a plurality of non-contact holding portions at any position between a position where the bare optical fiber is formed and a position where the coating is performed. The non-contact holding portion includes a guide groove which guides the bare optical fiber, and an internal space portion into which a fluid is introduced from an outside, in the guide groove, and an outlet through which the fluid in the internal space portion is blown to float the bare optical fiber in the guide groove is formed.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed on Japanese Patent Application No. 2015-116629,filed on Jun. 9, 2015 the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a manufacturing method, a controldevice, and a manufacturing apparatus of an optical fiber.

Description of Related Art

In general, in order to manufacture an optical fiber, a fiber drawingmethod of drawing an optical fiber vertically downward from an opticalfiber preform along a straight path is employed.

For example, in order to manufacture an optical fiber 5 using amanufacturing apparatus shown in FIG. 6, an optical fiber preform 2 ismelted by a heating furnace 11 of a drawing unit 10 and a bare opticalfiber 3 is drawn vertically downward therefrom through drawing. The bareoptical fiber 3 is cooled by a cooling unit 120 and is thereafterprovided with a coating layer by a coating unit 30, thereby obtaining anoptical fiber intermediate body 4. The coating layer of the opticalfiber intermediate body 4 is cured by a curing unit 40, therebyobtaining an optical fiber 5. The optical fiber 5 is wound by a winder100 via a pulley 80 and a take-up unit 90.

Regarding a manufacturing method thereof, as a factor that affectsproductivity, there is a restriction on the height of the entire system.The height of the system is the main factor in the restriction ofproductivity because there is a need to ensure a sufficient distance forcooling the bare optical fiber obtained by drawing of the optical fiberpreform.

When a new facility including a building is established, suchrestriction can be relaxed. However, this requires an enormous cost.When the enhancement of productivity is further required in the future,there is need to establish a new facility at a higher cost.

As a method of relaxing such restriction, there is a method of using adirection conversion tool having a non-contact holding mechanism.

The non-contact holding mechanism is a mechanism for holding an objectunder the pressure of a fluid such as air in a non-contact manner, and adirection changing device (non-contact holding portion) having themechanism can change the direction of the bare optical fiber withoutcoming into contact with the bare optical fiber (bare fiber).

When the direction changing device is used, the direction of the bareoptical fiber drawn from the optical fiber preform along a first pathcan be changed to follow a second path that is different from the firstpath (for example, refer to Japanese Patent No. 5571958 and JapaneseUnexamined Patent Application, First Publication No. S62-003037).

Japanese Patent No. 5571958 discloses a manufacturing method of anoptical fiber in which a direction conversion tool that has a groove,into which an optical fiber is introduced, and has an opening formed inthe groove is used. In this method, gas introduced into the tool throughan inflow port is ejected from the opening such that the optical fiberis changed in direction in a state in which the optical fiber is floatedby the pressure of the gas.

A direction changing device described in Japanese Unexamined PatentApplication, First Publication No. S62-003037 has a guide groove whichguides the bare optical fiber, and gas outlets are formed at the bottomsurface and both side surfaces of the guide groove (see Example andFIGS. 3 and 4). In the manufacturing method using the direction changingdevice, the direction of the optical fiber is changed in a state inwhich the optical fiber is floated by the pressure of the gas blown fromthe four outlets.

The floatation amount of the bare optical fiber is determined by thebalance between the pressure of the gas blown from the inside of thegroove of the non-contact holding mechanism, a drawing tension appliedto the bare optical fiber, and the like. Therefore, when conditions suchas the flow velocity of the gas at the non-contact holding mechanism anddrawing tension of the bare optical fiber are constant, the floatationamount of the bare optical fiber becomes constant, resulting in stabledrawing.

However, in an actual manufacturing process, due to a variation in theouter diameter of the optical fiber preform, a variation in the drawingvelocity of the bare optical fiber, and a decrease in the remaininglength of the optical fiber preform, a variation of drawing tensionduring drawing occurs. As a result, the floatation amount of the bareoptical fiber may be varied.

When the floatation amount of the bare optical fiber is varied,oscillation (variation) of the bare optical fiber increases in a grooveof the tool. Therefore, there is concern that the bare optical fiber maycome into contact with the inner surface of the groove of the tool. Whenthe bare optical fiber comes into contact with the tool, the bareoptical fiber is damaged, and there is a possibility that the strengththereof may decrease.

In addition, when the floating position of the bare optical fiber ischanged in the non-contact holding mechanism, the position of the bareoptical fiber introduced into the coating unit provided on thedownstream side of the non-contact holding mechanism varies, and thereis concern that the thickness of the coating may become uneven.

The present invention has been made taking the foregoing circumstancesinto consideration, and provides a manufacturing method, a controldevice, and a manufacturing apparatus of an optical fiber which achievethe stabilization of a floating position of a bare optical fiber at anon-contact holding portion.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a manufacturing method of anoptical fiber. The method includes drawing an optical fiber preform andforming a bare optical fiber, coating an outer circumference of the bareoptical fiber with a coating layer including a resin, and holding thebare optical fiber using one or a plurality of non-contact holdingportions at any position between a position where the bare optical fiberis formed and a position where the coating is performed. The non-contactholding portion includes a guide groove which guides the bare opticalfiber, and an internal space portion into which a fluid is introducedfrom an outside, in the guide groove, an outlet through which the fluidin the internal space portion is blown to float the bare optical fiberin the guide groove is formed, and a floatation position of the bareoptical fiber at at least one of the non-contact holding portions isdetected, the detected floatation position and a predetermined referencefloatation position are compared, and a flow rate of the fluidintroduced into the non-contact holding portions is controlled such thata deviation between the detected floatation position and the referencefloatation position is reduced.

In a second aspect of the present invention according to themanufacturing method of an optical fiber of the first aspect describedabove, it is preferable that the reference floating position is set onthe basis of a standard deviation of the floating amount of the bareoptical fiber determined by a preliminary test.

In a third aspect of the present invention according to themanufacturing method of an optical fiber of the first aspect or thesecond aspect described above, when a floatation amount of the bareoptical fiber becomes greater than a floatation amount at the referencefloating position and a standard deviation of the floatation amount ofthe bare optical fiber is greater than a standard deviation at thereference floating position, it is preferable that a flow rate of thefluid introduced into the non-contact holding portions is decreased.

In a fourth aspect of the present invention according to themanufacturing method of an optical fiber of the first aspect or thesecond aspect described above, when a floatation amount of the bareoptical fiber becomes smaller than a floatation amount at the referencefloating position and a standard deviation of the floatation amount ofthe bare optical fiber is greater than a standard deviation at thereference floating position, it is preferable that a flow rate of thefluid introduced into the non-contact holding portions is increased.

A fifth aspect of the present invention is a control device which isused in a manufacturing apparatus of an optical fiber. The manufacturingapparatus includes a drawing unit which draws an optical fiber preformand forms a bare optical fiber, and a coating unit which coats an outercircumference of the bare optical fiber with a coating layer comprisinga resin. The control device includes one or a plurality of non-contactholding portions which hold the bare optical fiber at any positionbetween the drawing unit and the coating unit, a position detection unitwhich detects a floating position of the bare optical fiber in thenon-contact holding portion, and a control unit which controls a flowrate of a fluid introduced into the non-contact holding portion on thebasis of the floating position detected by the position detection unit.The non-contact holding portion includes a guide groove which guides thebare optical fiber and an internal space portion into which the fluid isintroduced from the outside. In the guide groove, an outlet throughwhich the fluid in the internal space portion is blown to float the bareoptical fiber in the guide groove is formed. The control unit detectsthe floating position of the bare optical fiber at at least one of thenon-contact holding portions, compares the detected floating positionwith a predetermined reference floating position, and controls a flowrate of the fluid introduced into the non-contact holding portions so asto reduce the difference between the detected floating position and thepredetermined reference floating position.

In a sixth aspect of the present invention according to the controldevice of the fifth aspect described above, the reference floatingposition is set on the basis of a standard deviation of the floatingamount of the bare optical fiber determined by a preliminary test.

In a seventh aspect of the present invention according to the controldevice of the fifth aspect or the sixth aspect described above, when afloatation amount of the bare optical fiber becomes greater than afloatation amount at a reference floating position and a standarddeviation of the floatation amount of the bare optical fiber is greaterthan a standard deviation at the reference floating position, thecontrol unit decreases a flow rate of the fluid introduced into thenon-contact holding portions.

In an eighth aspect of the present invention according to the controldevice of the fifth aspect or the sixth aspect described above, when afloatation amount of the bare optical fiber becomes smaller than afloatation amount at a reference floating position and a standarddeviation of the floatation amount of the bare optical fiber is greaterthan a standard deviation at the reference floating position, thecontrol unit increases a flow rate of the fluid introduced into thenon-contact holding portions.

A ninth aspect of the present invention is a manufacturing apparatus ofan optical fiber includes the control device according to any one of thefifth aspect to the eighth aspect described above, the drawing unitwhich draws an optical fiber preform and forms the bare optical fiber,and the coating unit which coats the outer circumference of the bareoptical fiber with the coating layer comprising the resin.

According to the aspect of the present invention, the detected floatingposition and the predetermined reference floating position are comparedand the flow rate of the fluid introduced into the direction changingdevices is controlled so as to reduce the difference between thedetected floating position and the predetermined reference floatingposition. Therefore, the floatation amount of the bare optical fiber 3can be adjusted, and variation of the floatation amount can be reduced.

In detail, in the floatation amount of the bare optical fiber, there arelarge variation of the floatation amount due to the variation of thedrawing tension and fine variation of the floatation amount due to fineoscillation of the bare optical fiber. In the the present invention,both of the two variations of the floatation amount can be reduced bycontrolling the flow rate of the introduced fluid.

Therefore, the contact between the bare optical fiber and an inner sidesurface of the guide groove due to an insufficient floatation amountcaused by a variation in the outer diameter of the bare optical fibercan be avoided.

Therefore, the bare optical fiber is not damaged by the non-contactholding portion, and the operation ratio of the manufacturing apparatusis increased, resulting in an enhancement of productivity. Therefore, areduction in manufacturing costs can be achieved. In addition, theoptical fiber can be manufactured with a good yield.

Furthermore, a floating position of the bare optical fiber at thenon-contact holding portion becomes stable, and thus the position of thebare optical fiber that enters the coating unit becomes constant.Therefore, the coating is prevented from having an uneven thickness, andthe optical fiber with stable quality can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the schematic configuration of anembodiment of a manufacturing apparatus of an optical fiber of thepresent invention.

FIG. 2 is a schematic view showing the sectional structure of adirection changing device of the manufacturing apparatus shown in FIG.1.

FIG. 3 is a front view showing an example of the direction changingdevice.

FIG. 4 is a front view showing a modification example of the directionchanging device shown in FIG. 3.

FIG. 5 is a graph showing experimental results.

FIG. 6 is a schematic view showing an example of a manufacturingapparatus of an optical fiber in the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view showing the schematic configuration of amanufacturing apparatus 1 which is an embodiment of a manufacturingapparatus of an optical fiber according to the present invention.

The manufacturing apparatus 1 includes, in the order from the upstreamside toward the downstream side in a drawing direction, a drawing unit10, direction changing devices 20 (20A and 20B), a coating unit 30, acuring unit 40, a position detection unit 50 (50A and 50B), a controlunit 60, flow rate regulators 70 (70A, 70B), a pulley 80, a take-up unit90, and a winder 100.

The direction changing devices 20, the position detection unit 50, thecontrol unit 60, and the flow rate regulators 70 constitute a controldevice 101.

A downstream direction in a drawing direction is not a constantdirection. After the direction of the bare optical fiber 3 is changed bythe direction changing device 20, the changed direction is thedownstream direction.

The drawing unit 10 includes a heating furnace 11, and an optical fiberpreform 2 is heated by the heating furnace 11 to form a bare opticalfiber 3 through drawing.

A tip end portion 2 a is the tip end portion of a narrowed portion(neck-down) of the optical fiber preform 2 which is heated and melted.

The direction changing device (non-contact holding portion) 20 changesthe direction of the bare optical fiber 3. In the manufacturingapparatus 1 shown in FIG. 1, the two direction changing devices 20 areused. The direction changing devices 20 include the first directionchanging device (first non-contact holding portion) 20A and the seconddirection changing device (second non-contact holding portion) 20B inthe order from the upstream side to the downstream side in the drawingdirection.

The first direction changing device 20A allows the bare optical fiber 3drawn vertically downward (first path L1) from the optical fiber preform2 to be changed in direction by 90° and be directed horizontally (secondpath L2).

A plane including the first path L1 and the second path L2 is referredto as P1. An X direction is a direction along the second path L2 in theplane P1, and a Y direction is a direction perpendicular to the planeP1.

The second direction changing device 20B allows the bare optical fiber 3to be directed vertically downward (third path L3) by changing thedirection of the bare optical fiber 3 by 90°.

Hereinafter, the structure of the direction changing device 20 will bedescribed.

A direction changing device 201 shown in FIG. 3 is a first example ofthe direction changing device 20, and can change the direction of thebare optical fiber 3 by 90°.

The direction changing device 201 is formed in a quadrant shape in aplan view, and has a guide groove 21 formed in an outer circumferentialsurface 20 a along the entire circumferential length. The directionchanging device 201 is provided in a posture such that the center axisdirection thereof is coincident with the Y direction, and a radialdirection R (see FIG. 2) is directed along the plane P1 (see FIG. 1).Here, a direction along the outer circumferential surface 20 a having anarc shape in the plan view is referred to as a circumferentialdirection.

In the bottom portion of the guide groove 21, an outlet 22 for a fluid(air or the like) for floating the bare optical fiber 3 disposed alongthe guide groove 21 is formed along the guide groove 21. The outlet 22is formed over the entire length of the guide groove 21.

One end 22 a of the outlet 22 reaches a first end 21 a of the guidegroove 21, and a second end 22 b reaches the other end 21 b.

As shown in FIG. 2, the direction changing device 201 is configured todischarge the fluid (for example, air) in an internal space portion(fluid accumulation portion 25) ensured in the direction changing device201 toward the inside of the guide groove 21 through the outlet 22.

The direction changing device 201 may be configured to allow the fluidto be introduced into the fluid accumulation portion 25 from the outsideand be discharged to the guide groove 21 through the outlet 22.

As shown in FIG. 3, in the direction changing device 201, it ispreferable that an introduction portion 27 to which an introduction path26 that introduces the fluid to the fluid accumulation portion 25 fromthe outside is connected is formed. The introduction portion 27 is, forexample, an introduction port for the fluid.

As shown in FIG. 2, it is preferable that the guide groove 21 is formedto be inclined with respect to the radial direction R such that theinterval (a dimension in the Y direction) between inner side surfaces 21c and 21 c gradually increases toward the outside in the radialdirection. It is preferable that the two inner side surfaces 21 c and 21c have the same inclination angle θ with respect to the radial directionR.

In the direction changing device 201 shown in FIG. 3, the bare opticalfiber 3 enters one end 21 a of the guide groove 21 having a quadrantshape and exits the other end 21 b such that the change in direction by90° is achieved. A wire entrance portion 23 that the bare optical fiber3 enters is a portion including the first end 21 a of the guide groove21, and a wire exit portion 24 that the bare optical fiber 3 exits is aportion including the second end 21 b of the guide groove 21.

A direction changing device 202 shown in FIG. 4 is a modificationexample of the direction changing device 201 and has a ¾ circle shape inthe plan view. Hereinafter, like elements having the same configurationsas those of the above-described configuration are denoted by likereference numerals, and a description thereof will be omitted.

The direction changing device 202 has a structure in which, to the wireentrance side and the wire exit side of a body portion 29 a having thesame structure as that of the direction changing device 201, auxiliaryportions 29 b and 29 c having the same structure as that of the bodyportion 29 a are connected. The direction changing device 202 enters theguide groove 21 of the body portion 29 a through a wire entrance portion23′ of the bare optical fiber 3, is changed in direction by 90° in thebody portion 29 a, then exits a wire exit portion 24′. Therefore, thebasic function thereof is the same as that of the direction changingdevice 201.

The direction changing device 201 or 202 can change the direction of thebare optical fiber 3 by 90° and thus can be used as the directionchanging device 20A or 20B shown in FIG. 1.

As shown in FIG. 1, the position detection unit 50 includes a firstposition detection unit 50A and a second position detection unit 50B.

The first position detection unit 50A is provided on the downstream sidein the drawing direction of the second direction changing device 20A,and detects the position of the bare optical fiber 3 on the second pathL2.

The second position detection unit 50B is provided on the downstreamside in the drawing direction of the second direction changing device20B, and detects the position of the bare optical fiber 3 on the thirdpath L3.

As the first position detection unit 50A and the second positiondetection unit 50B, for example, a laser (optical) position sensor maybe used. For example, the laser position sensor can receive light thatis emitted toward the bare optical fiber 3 from a light source (laserlight source) with a detector provided to oppose the light source andcan detect the position of the bare optical fiber 3 on the basis of thelight.

When the floatation amount of the bare optical fiber 3 in the firstdirection changing device 20A fluctuates, the position in the Zdirection (a direction perpendicular to the X direction and the Ydirection) of the bare optical fiber 3 on the second path L2 is changed.Therefore, the first position detection unit 50A can detect thefloatation amount (floating position) of the bare optical fiber 3 in thefirst direction changing device 20A.

When the floatation amount of the bare optical fiber 3 in the seconddirection changing device 20B fluctuates, the position in the Xdirection of the bare optical fiber 3 on the third path L3 is changed.Therefore, the second position detection unit 50B can detect thefloatation amount of the bare optical fiber 3 in the second directionchanging device 20B.

The first position detection unit 50A and the second position detectionunit 50B outputs a position signal (detection signal) to the controlunit 60 on the basis of the information regarding the position of thebare optical fiber 3 (the result of the detection of the position of thebare optical fiber 3).

The flow rate regulator 70 can regulate the flow rate of the fluidintroduced into the direction changing devices 20A and 20B. For example,the flow rate regulators 70 may be provided on introduction paths (forexample, the introduction path 26 shown in FIG. 3) on which the fluid isintroduced into the direction changing devices 20A and 20B. As the flowrate regulator 70, a mass flow controller (MFC) or the like may be used.

In the manufacturing apparatus 1 shown in FIG. 1, the two flow rateregulators 70 are used. In the two flow rate regulators 70, the flowrate regulator 70 which regulates the flow rate of the fluid introducedinto the first direction changing device 20A is referred to as the firstflow rate regulator 70A, and the flow rate regulator 70 which regulatesthe flow rate of the fluid introduced into the second direction changingdevice 20B is referred to as the second flow rate regulator 70B.

The control unit 60 outputs control signals to the flow rate regulators70A and 70B on the basis of the position signal from the positiondetection unit 50 (50A, 50B), and the flow rate regulators 70A and 70Bcontrol the flow rate of the fluid introduced into the directionchanging devices 20A and 20B on the basis of the control signals,thereby controlling the floatation amount of the bare optical fiber 3 inthe direction changing devices 20A and 20B.

The coating unit 30 applies a coating material such as a urethaneacrylate-based resin to the outer circumference of the bare opticalfiber 3 to form a coating layer, thereby obtaining an optical fiberintermediate body 4.

The resin coating is, for example, a two-layer coating obtained byapplying a material for a primary coating layer having a low Young'smodulus to the inside and applying a material for a secondary coatinglayer having a high Young's modulus to the outside. The material that isused is, for example, a UV-curable resin.

The coating unit 30 may have a configuration in which the primarycoating layer and the secondary coating layer are separately applied, ormay also have a configuration in which the primary coating layer and thesecondary coating layer are simultaneously applied.

The curing unit 40 includes one or a plurality of UV lamps 40 a andcures the coating layer of the optical fiber intermediate body 4 to formthe optical fiber 5. For example, the curing unit 40 includes theplurality of UV lamps 40 a provided with a space interposedtherebetween, through which the optical fiber intermediate body 4passes.

The pulley 80 can change the direction of the optical fiber 5.

The take-up unit 90 is, for example, a take-up capstan, and determinesthe drawing velocity. The drawing velocity is, for example, 1500 m/minor higher.

The winder 100 is, for example, a winding bobbin for winding the opticalfiber 5.

Next, an embodiment of a manufacturing method of an optical fiber of thepresent invention will be described by exemplifying a case of using themanufacturing apparatus 1.

(Drawing Process)

As shown in FIG. 1, in the drawing unit 10, the optical fiber preform 2is heated and the bare optical fiber 3 is formed through drawing.

The outer diameter of the optical fiber preform 2 is, for example, 100mm or greater, and the length of the optical fiber 5 produced from asingle optical fiber preform 2 is, for example, thousands of kilometers.

(Change in Direction by Direction Changing Devices)

The bare optical fiber 3 drawn vertically downward (the first path L1)from the optical fiber preform 2 is directed horizontally (the secondpath L2) by being changed in direction by 90° in the first directionchanging device 20A.

The bare optical fiber 3 is directed vertically downward (the third pathL3) by being changed in direction by 90° in the second directionchanging device 20B.

As shown in FIG. 2, in the direction changing devices 20A and 20B, thebare optical fiber 3 can be floated by discharging the fluid (forexample, air) in the fluid accumulation portion 25 toward the inside ofthe guide groove 21 through the outlet 22. Specifically, the differencein pressure between a deep portion 21 d and a shallow portion 21 e ofthe guide groove 21 is increased by the discharged air, and thus aradially outward force is exerted on the bare optical fiber 3, therebyfloating the bare optical fiber 3.

The direction of the bare optical fiber 3 can be changed by thedirection changing devices 20A and 20B without coming into contact withthe bare optical fiber 3. The direction changing devices 20A and 20Brarely apply resistance (for example, the rotational resistance of apulley) unlike a contact direction changing device (for example,pulley).

Since the direction of the bare optical fiber 3 is changed by thedirection changing devices 20A and 20B, a distance for sufficientlycooling the bare optical fiber is ensured without increasing the heightof the entire system, thereby enhancing productivity.

The first position detection unit 50A outputs the first position signalto the control unit 60 on the basis of the positional information of thebare optical fiber 3 on the second path L2. The first position signal isa signal corresponding to the position in the Z direction of the bareoptical fiber 3 in the guide groove 21 in the first direction changingdevice 20A.

The second position detection unit 50B outputs the second positionsignal to the control unit 60 on the basis of the positional informationof the bare optical fiber 3 on the third path L3. The second positionsignal is a signal corresponding to the position in the X direction ofthe bare optical fiber 3 in the guide groove 21 in the second directionchanging device 20B.

The control unit 60 outputs the control signals to the first flow rateregulator 70A on the basis of the first position signal and controls theflow rate of the fluid introduced into the first direction changingdevice 20A on the basis of the control signals. Accordingly, bycontrolling the flow velocity of the fluid discharged from the outlet 22to the guide groove 21 in the first direction changing device 20A, thefloatation amount of the bare optical fiber 3 in the first directionchanging device 20A is regulated.

The control unit 60 outputs the control signals to the second flow rateregulator 70B on the basis of the second position signal, and the secondflow rate regulator 70B controls the flow rate of the fluid introducedinto the second direction changing device 20B on the basis of thecontrol signals. Accordingly, by controlling the flow velocity of thefluid discharged from the outlet 22 to the guide groove 21 in the seconddirection changing device 20B, the floatation amount of the bare opticalfiber 3 in the second direction changing device 20B is regulated.

For example, in a case where the drawing tension is constant, thefloatation amount of the bare optical fiber 3 increases as the flowvelocity of the fluid at the direction changing devices 20A and 20Bincreases, and the floatation amount of the bare optical fiber 3decreases as the flow velocity of the fluid decreases. In a case wherethe flow velocity of the fluid is constant, the floatation amount of thebare optical fiber 3 decreases as the drawing tension increases, and thefloatation amount of the bare optical fiber 3 increases as the drawingtension decreases.

When the floatation amount is increased, a floating position of the bareoptical fiber 3 is unstable and the variation of the floating positionis likely to increase. On the other hand, when the floatation amount isdecreased, a floating position of the bare optical fiber 3 is unstableand the variation of the floating position is likely to increase.

The control unit 60 regulates the flow rate of the fluid introduced intothe direction changing devices 20A and 20B when the floating position ofa bare optical fiber 3 is deviated and the variation (standard deviationσ) of the floatation amount is greater than the variation in thereference floating position on the basis of, for example, the floatingposition (reference floating position) at the predetermined drawingvelocity and drawing tension. Accordingly, the flow velocity of thefluid discharged from the outlet 22 to the guide groove 21 is adjustedand the floatation amount of the bare optical fiber 3 is adjusted. Adetailed description is provided below.

First, an example of a method of determining a reference floatingposition is described.

FIG. 5 is a graph showing a relationship between the standard deviationσ of the floatation amount of the bare optical fiber in a referencedrawing condition and an average floating position at a constant time.Since the standard deviation σ of the floatation amount is an index ofthe variation of the floatation amount, the floatation becomes stable asthe standard deviation σ is reduced. The floating position shows aposition in a radial direction (radial position) in the directionchanging devices.

The reference drawing condition is defined by the predetermined drawingvelocity (reference drawing velocity), the predetermined drawing tension(reference drawing tension), and the like. For example, as a referencedrawing condition, the drawing velocity of 30 m/s, the drawing tensionof 150 gf, the outer diameter of the bare optical fiber 3 of 125 μm andthe like can be employed.

The floating position where the standard deviation σ of the floatationamount is a minimum can be a reference floating position. For example,in FIG. 5, a position where the standard deviation σ of the floatationamount is a minimum is “P1” (the floating position: −1.79 mm), and theposition p1 can be a reference floating position.

The reference floating position can be defined on the basis of anaverage value of the standard deviation σ in a partial range in theradial direction in the direction changing devices. For example, in FIG.5, the average value of the standard deviation σ in the range E1 (thefloating position: −1.94 mm to −1.64 mm) is lower than in other rangeshaving the same width. The position p1 which is a center value (or aminimum value) of the range E1 can be defined as “a reference floatingposition”. In addition, the range E1 may be defined as “a referencefloating position”.

The standard deviation σ in the range E1 is smaller than a standarddeviation σ in other ranges having the same width where an averagefloating position is smaller than in the range E1 and a standarddeviation σ in other ranges where an average floating position isgreater than in the range E1. Therefore, the range E1 can be a rangewhere the standard deviation σ is a minimum.

The reference floating position becomes reproducibly constant whenmanufacturing conditions (drawing velocity, drawing tension, an outerdiameter of the bare optical fiber, and the like) are constant in thesame direction changing device. The reference floating position can bedetermined by the preliminary test.

The floating position can be variable by the manufacturing conditionssince the position depends on an installed location of the positiondetection unit; however, the position can be compared mutually under thesame conditions.

Next, a controlling method when the floating position of a bare opticalfiber 3 is deviated from the reference floating position is described.

Due to the changes of the drawing conditions (drawing velocity, drawingtension, and the like) from the reference drawing conditions, thefloating position of a bare optical fiber 3 may be deviated from thereference floating position. In this case, a position signal output fromthe position detection unit 50 is changed. The position signal is inputto the control unit 60, and the control unit 60 calculates the standarddeviation σ every predetermined setting time.

The feedback control can be fast as the setting time is shorter;however, the number of calculated data is also smaller and a calculationerror becomes greater. On the other hand, the time is longer, thefeedback is slower which is not preferable.

Therefore, the setting time is preferably selected in consideration ofthe reference drawing conditions. For example, the datum of the floatingposition of the bare optical fiber 3 is obtained in every 10 msec, andthe data processing is performed in every 10 sec (i.e., every 1000data). Thereby, the standard deviation σ can be determined.

As a standard of the variation of the floating position, it is notlimited to a standard deviation. Dispersion or a variation coefficientcan also be employed.

In a case where the floatation amount of the bare optical fiber 3becomes greater than the floatation amount at the reference floatingposition and the variation (standard deviation σ) of the floatationamount is greater than the variation at the reference floating position,the control unit 60 decreases the flow rate of the fluid introduced intothe direction changing devices 20A and 20B using the flow rateregulators 70A and 70B. Accordingly, the deviation between thefloatation amount of the bare optical fiber 3 and the floatation amountat the reference floating position is reduced.

By decreasing the flow rate of the fluid introduced into the directionchanging devices 20A and 20B, the flow velocity of the fluid dischargedfrom the outlet 22 to the guide groove 21 can be reduced, the floatationamount of the bare optical fiber 3 can be suppressed, and the variationof the floatation amount can be reduced.

On the other hand, in a case where the floatation amount of the bareoptical fiber 3 becomes smaller than the floatation amount at thereference floating position and the variation of the floatation amountis greater than the variation at the reference floating position, thecontrol unit 60 increases the flow rate of the fluid introduced into thedirection changing devices 20A and 20B using the flow rate regulators70A and 70B. Accordingly, the deviation between the floatation amount ofthe bare optical fiber 3 and the reference floating position is reduced.

By increasing the flow rate of the fluid introduced into the directionchanging devices 20A and 20B, the flow velocity of the fluid dischargedfrom the outlet 22 to the guide groove 21 is increased, and aninsufficient floatation amount of the bare optical fiber 3 is preventedas well as the variation of the floatation amount can be reduced.

As a control method, feedback control such as PID control is preferable.Accordingly, the flow rate of the fluid can be controlled with goodresponsiveness.

(Coating Process)

In the coating unit 30, the outer circumference of the bare opticalfiber 3 is coated with a coating material such as a urethaneacrylate-based resin to form the coating layer, thereby obtaining theoptical fiber intermediate body 4.

(Curing Process)

In the curing unit 40, the coating layer of the optical fiberintermediate body 4 is cured by being irradiated by the UV lamps 40 a,thereby obtaining the optical fiber 5.

The optical fiber 5 is changed in direction by the pulley 80, is takenup by the take-up unit 90, and is wound by the winder 100.

In the manufacturing method of the present embodiment, the detectedfloating position and the predetermined reference floating position arecompared and the flow rate of the fluid introduced into the directionchanging devices 20 is controlled so as to reduce the difference betweenthe detected floating position and the predetermined reference floatingposition. Therefore, the floatation amount of the bare optical fiber 3can be adjusted, and variation of the floatation amount can be reduced.

In detail, in the floatation amount of the bare optical fiber 3, thereare large variation of the floatation amount due to the variation of thedrawing tension and fine variation of the floatation amount due to fineoscillation of the bare optical fiber 3. In the manufacturing method ofthe present embodiment, both of the two variations of the floatationamount can be reduced by controlling the flow rate of the introducedfluid.

Therefore, the contact between the bare optical fiber 3 and the innerside surface 21 c of the guide groove 21 can be avoided.

Therefore, the bare optical fiber 3 is not damaged by the directionchanging devices 20A and 20B, and the operation ratio of themanufacturing apparatus 1 is increased, resulting in the enhancement ofproductivity. Therefore, a reduction in manufacturing costs can beachieved. In addition, the optical fiber 5 can be manufactured with agood yield.

Furthermore, the floating position of the bare optical fiber 3 in thedirection changing devices 20A and 20B becomes stable, and thus theposition of the bare optical fiber 3 that enters the coating unit 30becomes constant. Therefore, the coating is prevented from having anuneven thickness, and the optical fiber 5 with stable quality can bemanufactured.

EXAMPLE Example 1

The manufacturing apparatus 1 shown in FIG. 1 was prepared. As thedirection changing devices 20A and 20B, the direction changing device201 shown in FIG. 3 was used.

As shown in FIG. 2, the inclination angle θ of the inner side surface 21c of the guide groove 21 with respect to the radial direction R was setto 0.5°. The width of the bottom of the guide groove 21 was set to 50μm.

As the fluid introduced into the direction changing devices 20A and 20B,air was used.

In a preliminary test, the datum of the floating position of the bareoptical fiber 3 is obtained in every 10 msec, and the data processing isperformed in every 10 sec (i.e., every 1000 data). As a result, areference floating position at the first direction changing device 20Awas a position of a floating turning radius of 62.0 mm, and at thisposition, a standard deviation σ was a minimum value of 0.01 mm. A flowrate of the introduced air was 120 SLM. The reference floating positionat the second direction changing device 20B was a position of a floatingturning radius of 62.5 mm, and at this position, a standard deviation σwas a minimum value of 0.01 mm. A flow rate of the introduced air was130 SLM.

The first direction changing device 20A was provided at a position atwhich the temperature of the bare optical fiber 3 reached approximately1000° C. The second direction changing device 20B was provided at aposition separated by 1 m from the first direction changing device 20Aon the downstream side in the drawing direction.

The bare optical fiber 3 (with an outer diameter of 125 μm) was obtainedthrough drawing of the optical fiber preform 2 in the drawing unit 10.

The bare optical fiber 3 drawn vertically downward (the first path L1)from the optical fiber preform 2 was changed in direction to ahorizontal direction (the second path L2) by the first directionchanging device 20A, and was thereafter changed in direction to avertically downward direction (the third path L3) by the seconddirection changing device 20B.

In the coating unit 30, the bare optical fiber 3 was coated with theUV-curable resin, and the coating layer was cured by being irradiatedwith UV light by the UV lamps 40 a in the curing unit 40, therebyobtaining the optical fiber 5.

The optical fiber 5 was wound by the winder 100 via the pulley 80 andthe take-up unit 90.

When the floating position of the bare optical fiber 3 became greaterthan the reference floating position and the standard deviation σ of thefloatation amount was greater than the standard deviation σ at thereference floating position, the control unit 60 decreased the flow rateof the fluid introduced into the direction changing devices 20A and 20Busing the flow rate regulators 70A and 70B. Accordingly, the flowvelocity of the fluid discharged from the outlet 22 to the guide groove21 was reduced, the floatation amount of the bare optical fiber 3 wassuppressed, and the variation of the floatation amount was reduced.

When the floating position of the bare optical fiber 3 became smallerthan the reference floating position and the standard deviation σ of thefloatation amount was greater than the standard deviation σ at thereference floating position, the control unit 60 increased the flow rateof the fluid introduced into the direction changing devices 20A and 20Busing the flow rate regulators 70A and 70B. Accordingly, the flowvelocity of the fluid discharged from the outlet 22 to the guide groove21 was increased, the floatation amount of the bare optical fiber 3 wasincreased, and the variation of the floatation amount was reduced.

As the control method, PID control was employed.

By the manufacturing method described above, the optical fiber 5 havinga total length of 10,000 km was manufactured by using 10 optical fiberpreforms 2.

The linear velocity (drawing velocity) of the optical fiber 5 was 30m/s±1 m/s, and the drawing tension was 150±25 gf.

In the direction changing devices 20A and 20B, there was no significantvariation in the floating turning radius of the bare optical fiber 3,and the bare optical fiber 3 was stably floated.

In the manufacturing method, the optical fiber 5 was manufactured, and aproof test was conducted. As a result, it was confirmed that the opticalfiber 5 could be manufactured with a good yield without damaging thebare optical fiber 3 by the direction changing devices 20A and 20B.

Comparative Example 1

The flow rate of the air introduced into the first direction changingdevice 20A was a constant value (120 SLM) and the flow rate of the airintroduced into the second direction changing device 20B was a constantvalue (130 SLM), and the optical fiber 5 was manufactured. The otherconditions were similar to those of Example 1.

The drawing velocity of the optical fiber 5 was 30 m/s±1 m/s, and thedrawing tension was 150 gf±25 gf. When the drawing tension varied, avariation in the floatation amount of the bare optical fiber 3 was seen.

As a result of a proof test, breaking of the bare optical fiber 3, whichwas thought to be caused by the contact between the bare optical fiber 3and the inner side surface of the guide groove, had occurred. Therefore,it could not be said that a good manufacturing yield was achieved.

While the manufacturing method and the manufacturing apparatus of theoptical fiber of the present invention have been described above, thepresent invention is not limited to the examples described above, andcan be appropriately modified without departing from the spirit of thepresent invention.

For example, the number of direction changing devices used in themanufacturing method of the optical fiber of the present invention maybe one or more. The two direction changing devices 20 are used in themanufacturing apparatus 1 shown in FIG. 1. However, the number ofdirection changing devices 20 may be one or an arbitrary number of threeor more.

In a case where a plurality of direction changing devices is present,the position of the bare optical fiber is detected by at least one ofthe plurality of direction changing devices. The position of the bareoptical fiber may be detected by all of the plurality of directionchanging devices or some direction changing devices among the pluralityof direction changing devices.

The flow rate of the introduced fluid is controlled preferably by all ofthe plurality of direction changing devices, but may also be controlledby some direction changing devices among the plurality of directionchanging devices. The flow rate of the introduced fluid is controlledpreferably by at least the direction changing device closest to thedownstream side.

In addition, the direction changing device can be disposed at anyposition between the heating furnace and coating unit.

While preferred embodiments of the invention have been described andshown above, it should be understood that these are exemplary of theinvention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

What is claimed is:
 1. A manufacturing method of an optical fiber, themethod comprising: drawing an optical fiber preform and forming a bareoptical fiber; coating an outer circumference of the bare optical fiberwith a coating layer comprising a resin; and holding the bare opticalfiber using one or a plurality of non-contact holding portions at anyposition between a position where the bare optical fiber is formed and aposition where the coating is performed, wherein: the non-contactholding portion comprises a guide groove which guides the bare opticalfiber, and an internal space portion into which a fluid is introducedfrom an outside; in the guide groove, an outlet through which the fluidin the internal space portion is blown to float the bare optical fiberin the guide groove is formed; and a floatation position of the bareoptical fiber at at least one of the non-contact holding portions isdetected, the detected floatation position and a predetermined referencefloatation position are compared, and a flow rate of the fluidintroduced into the non-contact holding portions is controlled such thata deviation between the detected floatation position and the referencefloatation position is reduced.
 2. The manufacturing method of anoptical fiber according to claim 1, wherein the reference floatingposition is set on the basis of a standard deviation of the floatingamount of the bare optical fiber determined by a preliminary test. 3.The manufacturing method of an optical fiber according to claim 1,wherein when a floatation amount of the bare optical fiber becomesgreater than a floatation amount at a reference floating position and astandard deviation of the floatation amount of the bare optical fiber isgreater than a standard deviation at the reference floating position, aflow rate of the fluid introduced into the non-contact holding portionsis decreased.
 4. The manufacturing method of an optical fiber accordingto claim 1, wherein when a floatation amount of the bare optical fiberbecomes smaller than a floatation amount at a reference floatingposition and a standard deviation of the floatation amount of the bareoptical fiber is greater than a standard deviation at the referencefloating position, a flow rate of the fluid introduced into thenon-contact holding portions is increased.
 5. A control device which isused in a manufacturing apparatus of an optical fiber, the manufacturingapparatus comprising: a drawing unit which draws an optical fiberpreform and forms a bare optical fiber; and a coating unit which coatsan outer circumference of the bare optical fiber with a coating layercomprising a resin, the control device comprising: one or a plurality ofnon-contact holding portions which hold the bare optical fiber at anyposition between the drawing unit and the coating unit; a positiondetection unit which detects a floating position of the bare opticalfiber in the non-contact holding portion; and a control unit whichcontrols a flow rate of a fluid introduced into the non-contact holdingportion on the basis of the floating position detected by the positiondetection unit, wherein the non-contact holding portion comprises aguide groove which guides the bare optical fiber and an internal spaceportion into which the fluid is introduced from the outside, wherein inthe guide groove, an outlet through which the fluid in the internalspace portion is blown to float the bare optical fiber in the guidegroove is formed, and wherein the control unit detects the floatingposition of the bare optical fiber at at least one of the non-contactholding portions, compares the detected floating position with apredetermined reference floating position, and controls a flow rate ofthe fluid introduced into the non-contact holding portions so as toreduce the difference between the detected floating position and thepredetermined reference floating position.
 6. The control deviceaccording to claim 5, wherein the reference floating position is set onthe basis of a standard deviation of the floating amount of the bareoptical fiber determined by a preliminary test.
 7. The control deviceaccording to claim 5, wherein when a floatation amount of the bareoptical fiber becomes greater than a floatation amount at a referencefloating position and a standard deviation of the floatation amount ofthe bare optical fiber is greater than a standard deviation at thereference floating position, the control unit decreases a flow rate ofthe fluid introduced into the non-contact holding portions.
 8. Thecontrol device according to claim 5, wherein when a floatation amount ofthe bare optical fiber becomes smaller than a floatation amount at areference floating position and a standard deviation of the floatationamount of the bare optical fiber is greater than a standard deviation atthe reference floating position, the control unit increases a flow rateof the fluid introduced into the non-contact holding portions.
 9. Amanufacturing apparatus of an optical fiber comprising: the controldevice according to claim 5; the drawing unit which draws an opticalfiber preform and forms the bare optical fiber; and the coating unitwhich coats the outer circumference of the bare optical fiber with thecoating layer comprising the resin.